The present invention relates to rotary fluid pressure devices, and more particularly, to such devices which include a pair of relatively rotatable valve members and a valve-seating mechanism operable to bias one of the valve members into tight, sealing engagement with the other valve member.
Although it will become apparent from the subsequent description of the invention that it may be useful with many types and configurations of rotary fluid pressure devices, including both pumps and motors, it is especially advantageous when used in a fluid motor, and will be described in connection therewith.
Also, although the invention may be used with devices having various types of fluid energy-translating displacement mechanisms, for example, axial piston devices, etc., the invention is especially adapted for use in a device including a gerotor displacement mechanism, and will be described in connection therewith.
Fluid motors of the type utilizing a gerotor displacement mechanism to convert fluid pressure into a rotary output are especially suited for low speed, high torque applications. Typically, in fluid motors of this type, the gerotor mechanism is of the type including a fixed internally toothed member (ring) and an externally toothed member (star) which is eccentrically disposed within the ring and orbits and rotates relative thereto. In fluid motors of this type there are normally two relatively movable valve members. One of the valve members is stationary and provides a fluid passage communicating with each of the volume chambers defined by the gerotor mechanism, while the other valve member rotates relative to the stationary valve member. If the rotatable valve member rotates at the orbiting speed of the star, the valving is referred to as "high speed", whereas if the valve member rotates at the rotational speed of the star, the valving is referred to as "low speed". Although the present invention may be used with motors having high speed valving, it is especially advantageous when used with low speed valving, and will be described in connection therewith.
A low speed, high torque gerotor motor of the type having low speed valving is illustrated in U.S. Pat. No. 3,572,983, assigned to the assignee of the present invention and incorporated herein by reference. Motors made in accordance with the cited patent constitute the known prior art relative to the present invention. Fluid motors made in accordance with the cited patent include, in addition to the previously mentioned stationary valve member and rotatable valve member, a valve-seating mechanism which is now generally well known in the art. The general function of the valve-seating mechanism is to exert a circumferentially-uniform biasing force, biasing the rotatable valve member into tight, sealing engagement with the stationary valve member.
One of the problems which has long been associated with fluid motors of the type described is a condition referred to as "stalling". Because the commutator valving action occurs at the plane surface of engagement of the two valve members, any axial separation of the two valve members will permit communication between high pressure fluid and low pressure fluid, thus eliminating the pressure differential across the gerotor mechanism, resulting in stalling. When stalling has occurred, it has generally been necessary to stop the flow of pressurized fluid to the motor, permitting the rotatable valve member to become reseated against the stationary valve member before starting operation again.
There have been several conditions believed to be responsible for this phenomenon of valve "lift-off" and stalling. Among these is excessive case pressure biasing the rotary valve away from the stationary valve. Another cause is believed to be manufacturing inaccuracies in the main spline connections which can result in a axial thrust force transmitted from the main drive shaft, through the valve drive shaft to the rotary valve. Attempts to overcome these and other suspected causes of valve lift-off have not previously been successful in eliminating the problem of stalling.
Accordingly, it is an object of the present invention to provide a rotary fluid pressure device in which the principal cause of stalling is determined and overcome.
It is a more specific object of the present invention to determine the existence of a cause for stalling which is unrelated to valve lift-off.